Internal combustion engines may include water injection systems that inject water into a plurality of locations, including an intake manifold, upstream of engine cylinders, or directly into engine cylinders. Injecting water into the engine intake air may increase fuel economy and engine performance, as well as decrease engine emissions. When water is injected into the engine intake or cylinders, heat is transferred from the intake air and/or engine components to the water. This heat transfer leads to evaporation, which results in cooling. Injecting water into the intake air (e.g., in the intake manifold) lowers both the intake air temperature and a temperature of combustion at the engine cylinders. By cooling the intake air charge, a knock tendency may be decreased without enriching the combustion air-fuel ratio. This may also allow for a higher compression ratio, advanced ignition timing, and decreased exhaust temperature. As a result, fuel efficiency is increased. Additionally, greater volumetric efficiency may lead to increased torque. Furthermore, lowered combustion temperature with water injection may reduce NOx, while a more efficient fuel mixture may reduce carbon monoxide and hydrocarbon emissions. As explained above, water may be injected into different locations, including the intake manifold, intake ports of engine cylinders, or directly into engine cylinders. While direct and port injection may provide increased cooling to the engine cylinders and ports, intake manifold injection may increase cooling of the charge air without needing high pressure injectors and pumps. However, due to the lower temperature of the intake manifold, not all the water injected at the intake manifold atomizes properly. Condensed water from water injection may accumulate within the intake manifold and result in unstable combustion if ingested by the engine. Additionally, manifold water injection may result in uneven water distribution amongst cylinders coupled to the manifold. As a result, uneven cooling may be provided to the engine cylinders.
Other approaches to reduce condensate formation in the intake manifold during water injection include limiting the amount of water injected based on manifold temperature. For example, the approach shown by Yacoub in U.S. publication No. 2013/0206100 determines the amount of water to be injected as a function of measured manifold temperature. However, the inventors have recognized potential issues with such methods. In particular, adjusting water injection amounts based on manifold temperature alone may not sufficiently reduce condensation and water accumulation in the intake manifold. Further, there is no way to compensate for water that condenses within the intake manifold. As a result, unstable combustion may result from water ingested by the engine.
In one example, the issues described above may be addressed by a method for injecting an amount of water into an intake manifold of an engine responsive to engine conditions and adjusting an engine operating parameter responsive to a first portion of the amount of water that vaporized and second portion of the amount of water that remained liquid. In this way, engine operation may be adjusted to compensate for the first and second portions, thereby decreasing the likelihood of unstable combustion due to condensed liquid in the intake manifold and increasing the fuel economy and engine performance benefits of water injection.
As one example, the first portion of the amount of water that vaporized may be determined based on a change in manifold temperature following the injecting and the second portion of the amount of water that remained liquid may be determined based on the injected amount of water and the first portion. Further, engine operating parameters such as spark timing may be adjusted in response to the first and second portions. In this way, spark timing adjustments may compensate for the condensed water resulting from water injection and therefore reduce the likelihood of unstable combustion due to ingesting the condensed water. In another example, water injection amounts for subsequent water injection events may be adjusted based on the first and/or second portions. This may result in achieving desired water injection amounts in the intake manifold and therefore further increase fuel economy, decrease knock, and decrease emissions.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.